Field of the Invention
The present invention relates to an organic light emitting display device.
Discussion of the Related Art
Recently, with the advancement of multimedia, the importance of flat panel display (FPD) devices is increasing. Therefore, various FPD devices such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, and organic light emitting display devices are being used practically. In such FPD devices, the organic light emitting display devices have a fast response time of 1 ms or less and low power consumption, and have no limitation in a viewing angle because the organic light emitting display devices self-emit light. Accordingly, the organic light emitting display devices are attracting much attention as next generation FPD devices.
General organic light emitting display devices include a display panel, including a plurality of pixels that are respectively formed a plurality of pixel areas defined by intersections between a plurality of data lines and a plurality of gate lines, and a panel driver that emits light from the plurality of pixels.
Each of the pixels of the display panel, as illustrated in FIG. 1, includes a switching transistor ST, a driving transistor DT, and a capacitor Cst, and a light emitting element OLED.
The switching transistor ST is turned on by a gate signal GS supplied from a gate line G, and supplies a data voltage Vdata, supplied from a data line D, to the driving transistor DT.
The driving transistor DT is turned on with the data voltage Vdata supplied from the switching transistor ST, and controls a data current Ioled which flows to the light emitting element OLED according to a driving voltage VDD supplied through a driving power line PL.
The capacitor Cst is connected between a gate and source of the driving transistor DT, stores a voltage corresponding to the data voltage Vdata supplied to the gate of the driving transistor DT, and turns on the driving transistor DT with the stored voltage.
The light emitting element OLED includes an anode electrode layer connected to the source of the driving transistor DT, a cathode electrode layer CE receiving a ground voltage, and an organic layer that includes a light emitting layer formed between the anode electrode layer and the cathode electrode layer. The light emitting element OLED emits light in proportion to the data current Ioled supplied from the driving transistor DT.
Each pixel of the general organic light emitting display device controls a level of the data current Ioled, which flows from the driving voltage VDD terminal to the light emitting element OLED, with a switching time of the driving TFT DT based on the data voltage Vdata to emit light from the light emitting element OLED, thereby displaying a certain image.
In the organic light emitting display device, an emission luminance of each pixel is affected by the data voltage Vdata and the driving voltage VDD. Therefore, the driving voltage VDD supplied to each pixel should be constant for a uniform luminance of each pixel.
However, the driving voltage VDD is a direct current (DC) voltage having a predetermined voltage level, and while the driving voltage VDD is supplied to each pixel through the driving power line PL, the driving voltage VDD is dropped by a line resistance of the driving power line PL. As organic light emitting display devices are enlarged in size, the drop of the driving voltage VDD more increases.
Therefore, a method for minimizing a drop of the driving voltage supplied to each pixel is needed.